Simplify ProblemBuilder#status method

Author: malczuuu

src/main/java/io/github/malczuuu/problem4j/core/ProblemBuilder.java

@@ -46,8 +46,7 @@ public interface ProblemBuilder {
   ProblemBuilder status(int status);
 
   /**
-   * Sets the HTTP status code using a {@link ProblemStatus} enum. It also sets {@link #title} if
-   * not already assigned.
+   * Sets the HTTP status code using a {@link ProblemStatus} enum.
    *
    * @param status the {@link ProblemStatus} representing the HTTP status
    * @return this builder instance for chaining
@@ -115,6 +114,20 @@ public interface ProblemBuilder {
   /**
    * Builds an immutable {@link Problem} instance with the configured properties and extensions.
    *
+   * <p>Default value evaluation (all defaults are applied at build time):
+   *
+   * <ul>
+   *   <li>If no type was provided, the resulting {@code Problem} will use {@code
+   *       Problem#BLANK_TYPE}.
+   *   <li>If no title was provided, but the numeric status corresponds to a known {@code
+   *       ProblemStatus}, the builder will use the matching {@code ProblemStatus#getTitle()} as the
+   *       problem title.
+   *   <li>The numeric status defaults to <code>0</code> when not set; a title will not be derived
+   *       from status when it is <code>0</code> or when it does not map to any known {@code
+   *       ProblemStatus}.
+   *   <li>Any extensions configured on the builder will be present on the created {@code Problem}.
+   * </ul>
+   *
    * @return a new {@link Problem} instance
    */
   Problem build();

src/main/java/io/github/malczuuu/problem4j/core/ProblemBuilderImpl.java

@@ -44,13 +44,7 @@ public ProblemBuilder status(int status) {
 
   @Override
   public ProblemBuilder status(ProblemStatus status) {
-    if (status != null) {
-      if (title == null) {
-        title = status.getTitle();
-      }
-      this.status = status.getStatus();
-    }
-    return this;
+    return status != null ? status(status.getStatus()) : status(0);
   }
 
   @Override

src/test/java/io/github/malczuuu/problem4j/core/ProblemBuilderImplTests.java

@@ -1,6 +1,7 @@
 package io.github.malczuuu.problem4j.core;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 
 import java.net.URI;
 import java.util.Arrays;
@@ -33,6 +34,51 @@ void givenNullProblemStatus_shouldNotSetTitleOrStatus() {
     assertThat(problem.getTitle()).isNull();
   }
 
+  @Test
+  void givenProblemStatus_shouldSetNumericStatusAndTitle() {
+    Problem problem = Problem.builder().status(ProblemStatus.BAD_REQUEST).build();
+
+    assertThat(problem.getStatus()).isEqualTo(ProblemStatus.BAD_REQUEST.getStatus());
+    assertThat(problem.getTitle()).isEqualTo(ProblemStatus.BAD_REQUEST.getTitle());
+  }
+
+  @Test
+  void givenProblemStatus_shouldPreferExplicitStatusValueWhenSetEarlier() {
+    Problem problem = Problem.builder().status(405).status(ProblemStatus.I_AM_A_TEAPOT).build();
+
+    assertThat(problem.getStatus()).isEqualTo(ProblemStatus.I_AM_A_TEAPOT.getStatus());
+    assertThat(problem.getTitle()).isEqualTo(ProblemStatus.I_AM_A_TEAPOT.getTitle());
+  }
+
+  @Test
+  void givenExplicitTitle_thenStatusProblemStatus_shouldNotOverrideTitle() {
+    Problem problem =
+        Problem.builder().title("Custom Title").status(ProblemStatus.BAD_REQUEST).build();
+
+    assertThat(problem.getStatus()).isEqualTo(ProblemStatus.BAD_REQUEST.getStatus());
+    assertThat(problem.getTitle()).isEqualTo("Custom Title");
+  }
+
+  @Test
+  void givenStatusProblemStatus_thenExplicitTitle_shouldOverrideDerivedTitle() {
+    Problem problem = Problem.builder().status(ProblemStatus.NOT_FOUND).title("My Title").build();
+
+    assertThat(problem.getStatus()).isEqualTo(ProblemStatus.NOT_FOUND.getStatus());
+    assertThat(problem.getTitle()).isEqualTo("My Title");
+  }
+
+  @Test
+  void givenInvalidTypeString_shouldThrowIllegalArgumentException() {
+    assertThatThrownBy(() -> Problem.builder().type("ht tp://not a uri"))
+        .isInstanceOf(IllegalArgumentException.class);
+  }
+
+  @Test
+  void givenInvalidInstanceString_shouldThrowIllegalArgumentException() {
+    assertThatThrownBy(() -> Problem.builder().instance("::://invalid"))
+        .isInstanceOf(IllegalArgumentException.class);
+  }
+
   @Test
   void givenNullURIInstance_shouldNotSetIt() {
     Problem problem = Problem.builder().instance((URI) null).build();
@@ -107,4 +153,58 @@ void givenCollectionWithNullElement_shouldIgnoreNullElement() {
 
     assertThat(problem.getExtensions()).containsExactlyInAnyOrder("x", "y");
   }
+
+  @Test
+  void numericStatus_shouldDeriveTitleWhenKnown() {
+    Problem problem = Problem.builder().status(ProblemStatus.MULTI_STATUS.getStatus()).build();
+
+    assertThat(problem.getStatus()).isEqualTo(ProblemStatus.MULTI_STATUS.getStatus());
+    assertThat(problem.getTitle()).isEqualTo(ProblemStatus.MULTI_STATUS.getTitle());
+  }
+
+  @Test
+  void unknownNumericStatus_shouldNotDeriveTitle() {
+    Problem problem = Problem.builder().status(999).build();
+
+    assertThat(problem.getStatus()).isEqualTo(999);
+    assertThat(problem.getTitle()).isNull();
+  }
+
+  @Test
+  void typeAndInstance_stringOverloads_shouldAcceptValidUris() {
+    String t = "http://example.org/type";
+    String i = "http://example.org/instance";
+
+    Problem problem = Problem.builder().type(t).instance(i).build();
+
+    assertThat(problem.getType()).isEqualTo(URI.create(t));
+    assertThat(problem.getInstance()).isEqualTo(URI.create(i));
+  }
+
+  @Test
+  void emptyMapExtension_shouldBeIgnored() {
+    Map<String, Object> m = new HashMap<>();
+    Problem problem = Problem.builder().extension(m).build();
+
+    assertThat(problem.getExtensions()).isEmpty();
+  }
+
+  @Test
+  void nullValuedExtension_isPresentButOmittedFromToString() {
+    Problem problem = Problem.builder().extension("ext", null).build();
+
+    assertThat(problem.getExtensions()).containsExactly("ext");
+    assertThat(problem.getExtensionValue("ext")).isNull();
+
+    String s = problem.toString();
+    assertThat(s).doesNotContain("\"ext\"");
+  }
+
+  @Test
+  void laterExtensions_shouldOverwriteEarlierValues() {
+    Problem problem =
+        Problem.builder().extension("k", "v1").extension(Problem.extension("k", "v2")).build();
+
+    assertThat(problem.getExtensionValue("k")).isEqualTo("v2");
+  }
 }